In coils for the electrical or electronic equipment, including inverter-related equipment, such as high-speed switching devices, inverter motors, transformers, and the like, there are used, as a magnet wire, insulated electric wires (insulated wires) composed of a so-called enamel wire, insulated wires having multi-covering layers including a layer composed of an enamel resin and a covering layer composed of another kind of resin other than the enamel resin, and the like.
In regard to coils for the electrical or electronic equipment, various techniques have been developed in order to immobilize the insulated wire (winding wire) or to enhance the insulation property. For example, Patent Literature 1 discloses a technique of disposing an insulating paper at coil housing grooves formed at a stator core of a rotating electric motor, immobilizing the coil at the coil housing groove using a varnish, and thereby immobilizing the coil while providing insulation between the coil and the stator core. Patent Literature 2 discloses a prepreg sheet as a technique for preventing a contact between a stator core or a rotor core of a driving motor for a vehicle and a conductor coil.
Furthermore, an investigation has also been conducted to enhance the insulation property at a bent portion of an insulated wire. For example, Patent Literature 3 discloses a technique for preventing partial discharge in between adjacent coils or the like, by providing an additional insulating layer in predetermined regions of hypotenuse parts and bent parts of a segment coil.